Unraveling the role of superalkalis in modulating the static and dynamic hyperpolarizabilities of emerging calix[4]arenes

Abstract

Calixarenes, as novel organic materials, can play a pivotal role in the development of high-performance nonlinear optical materials due to the ease of design and fabrication. In this study, DFT simulations were employed to investigate the geometric, electronic, and NLO responses of calix[4]arene doped with Li₃O, Na₃O, and K₃O superalkalis. The computed values of the vertical ionization energies and interaction energies indicate the chemical and thermodynamic stabilities of the targeted M₃O@calix[4]arene complexes. The corresponding energy gaps (2.01 to 3.49 eV) are notably reduced, indicating the semiconductor nature of the materials. Surprisingly, the M₃O@calix[4]arene complexes exhibit transparency in the UV/visible range as the absorption peaks are shifted in the near infrared (NIR) region. The highest values of 5.9 × 10⁵ a.u. and 2.3 × 10⁸ a.u. for the respective first and second hyperpolarizabilities are observed for Na₃O@calix[4]arene. Furthermore, the Na₃O@calix[4]arene complex exhibits maximum values of 2.3 × 10⁵ a.u. for second harmonic generation (SHG) and (K₃O@calix[4]arene) 2.3 × 10⁶ a.u. for the electro-optical Pockels effect (EOPE) at 1064 nm. Similarly, approximations are made for the dynamic second hyperpolarizability coefficients (EOKE and EFISHG) at different wavelengths. Notably, the Na₃O@calix[4]arene complex demonstrates the highest quadratic nonlinear refractive index (n₂) of 9.5 × 10⁻¹⁵ cm² W⁻¹ at 1064 nm. This research paves the way for the development of stable calix[4]arenes doped with superalkalis, leading to an improved nonlinear optical (NLO) response.